1. Field of the Invention
The present invention relates to an image forming apparatus which uses a plurality of sheet processing apparatuses equipped with sheet processing functions and arranged and connected serially.
2. Description of the Related Art
Conventionally, an image forming apparatus connected with sheet processing apparatuses such as a finisher and sorter (sometimes called post-processing units) have been used for personal purposes and business purposes. Today, however, along with improvements in the image quality and increase in the speed of image forming apparatus, they are coming into use in the print industry as well.
In the print industry, various types of sheet processing (post-processing) are required for bookbinding. Typical sheet processing includes a stapling process, folding process, and punch process. Sometimes, multiple types of sheet processing are used in combination. In that case, it is preferable to serially arrange multiple sheet processing apparatuses with different sheet processing functions and connect them to an image forming apparatus (Japanese Patent Laid-Open No. 6-286931).
When using multiple sheet processing apparatuses, it is necessary to take into consideration processing time on each sheet processing apparatus and preparation time (start-up time) required for the sheet processing apparatus to get ready for processing. For example, if the image forming apparatus or an upstream sheet processing apparatus discharges a sheet to a sheet processing apparatus connected downstream even though the downstream sheet processing apparatus is not ready, troubles such as paper jam will occur.
To solve this, it is conceivable to discharge the sheet based on the last sheet processing apparatus that gets ready. However, this method can delay the timing of discharge and slow down the printing process if the last sheet processing apparatus is not in use. This results in low processing efficiency. That is, sheet processing apparatuses that finally stacks a sheet sometimes vary on a sheet-by-sheet basis, and thus appropriate timing of discharge can vary from sheet to sheet.
Thus, from all the sheet processing apparatuses serially arranged and connected, it is desirable to consider the preparation and processing time required to go from the sheet processing apparatus connected directly with the image forming apparatus, to the sheet processing apparatus which actually performs sheet processing.